**Marinate the Beef**:
- In a medium bowl, combine soy sauce, cornstarch, and rice vinegar. Add the thinly sliced beef to the marinade, tossing to coat. Let it marinate for at least 15 minutes.
**Prepare the Sauce**:
- In a small bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, rice vinegar, brown sugar, sesame oil, and beef broth or water. Set aside.
**Stir-Fry the Vegetables**:
- Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the broccoli florets, bell pepper, and carrot. Stir-fry for 4-5 minutes until the vegetables are tender-crisp. Remove the vegetables from the skillet and set aside.
**Stir-Fry the Beef**:
- In the same skillet, add the remaining 1 tablespoon of vegetable oil. Add the marinated beef in a single layer and cook until browned, about 2-3 minutes per side. Add the minced garlic and minced ginger to the skillet. Stir-fry for another 1-2 minutes.
**Combine and Cook**:
- Return the cooked vegetables to the skillet with the beef. Pour the sauce over the beef and vegetables, stirring to coat everything evenly. Cook for another 2-3 minutes, allowing the flavors to meld together. Stir in the chopped green onions.
**Serve**:
- Serve the beef and broccoli stir-fry hot over steamed rice or noodles.